Plasma etching method and plasma etching apparatus

ABSTRACT

A plasma etching method for plasma-etching an object including an etching target film and a patterned mask. The plasma etching method includes a first step of plasma-etching the etching target film using the mask, and a second step of depositing a silicon-containing film using plasma of a silicon-containing gas on at least a part of a side wall of the etching target film etched by the first step.

TECHNICAL FIELD

The present invention relates to a plasma etching method and a plasmaetching apparatus.

BACKGROUND ART

Due to the high-density integration of semiconductor devices in recentyears, wiring and separation widths of circuit patterns required forproducing semiconductor devices have become smaller. Typically, acircuit pattern is formed by etching a target film using a patternedmask.

To form a fine circuit pattern, it is necessary to reduce the minimumsize of a mask pattern and to accurately transfer openings with smallsizes to a target film.

However, when etching an organic mask made of, for example, an amorphouscarbon layer film (which is hereafter referred to as an “ACL film”),“bowing”, where the cross section of a part of an opening of the ACLfilm widens, may occur. When bowing occurs, the ACL film being etchedcollapses and the opening is closed. This, for example, may result in aproblem where a target film becomes unable to be etched.

Patent Document 1 discloses a technology for suppressing bowing by usingan oxygen gas (O₂) and a carbonyl sulfide (COS) gas as process gases.

RELATED-ART DOCUMENT Patent Document

-   [Patent Document 1] Japanese Laid-Open Patent Publication No.    2011-204999

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, although the technology disclosed by Patent Document 1 canreduce bowing, it still cannot solve the problem described above.

An aspect of this disclosure provides a plasma etching method that cansolve the above problem and can form a desired shape by etching.

Means for Solving the Problems

In an aspect of this disclosure, there is provided a plasma etchingmethod for plasma-etching an object including an etching target film anda patterned mask. The plasma etching method includes a first step ofplasma-etching the etching target film using the mask, and a second stepof depositing a silicon-containing film using plasma of asilicon-containing gas on at least a part of a side wall of the etchingtarget film etched by the first step.

Advantageous Effect of the Invention

An aspect of this disclosure makes it possible to provide a plasmaetching method that can form a desired shape by etching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an exemplary configuration ofa plasma etching apparatus according to an embodiment;

FIG. 2 is a flowchart illustrating an exemplary plasma etching methodaccording to an embodiment;

FIG. 3A is a drawing used to describe an exemplary plasma etching methodof an embodiment;

FIG. 3B is a drawing used to describe an exemplary plasma etching methodof an embodiment;

FIG. 3C is a drawing used to describe an exemplary plasma etching methodof an embodiment;

FIG. 3D is a drawing used to describe an exemplary plasma etching methodof an embodiment;

FIG. 3E is a drawing used to describe an exemplary plasma etching methodof an embodiment;

FIG. 4A is a SEM image used to describe an exemplary effect of a plasmaetching method of an embodiment;

FIG. 4B is a SEM image used to describe an exemplary effect of a plasmaetching method of an embodiment;

FIG. 5A is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 5B is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 5C is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 5D is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 6A is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 6B is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 6C is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 6D is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 7A is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 7B is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment;

FIG. 8A is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment; and

FIG. 8B is a SEM image used to describe another exemplary effect of aplasma etching method of an embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described below with referenceto the accompanying drawings. Throughout the specification and thedrawings, the same reference number is assigned to substantially thesame components, and repeated descriptions of those components areomitted.

<Plasma Etching Apparatus>

An overall configuration of a plasma etching apparatus that can performa plasma etching method of an embodiment is described. An exemplaryplasma etching apparatus used for descriptions in the presentapplication is a parallel-plate type plasma etching apparatus where anupper electrode and a lower electrode (susceptor) are disposed in achamber to face each other and a process gas is supplied through theupper electrode into the chamber.

FIG. 1 is a schematic diagram illustrating an exemplary configuration ofa plasma etching apparatus according to an embodiment.

A plasma etching apparatus 1 includes a chamber 10 comprised of aconductive material such as aluminum and a gas supply 15 for supplying aprocess gas into the chamber 10. An appropriate process gas is selectedaccording to the type of a mask, the type of a target film (a film to beetched), and so on.

The chamber 10 is electrically grounded. A lower electrode 20 and anupper electrode 25 are provided in the chamber 10. The upper electrode25 is disposed in parallel with and to face the lower electrode 20.

The lower electrode 20 also functions as a mount table for holding anobject to be processed, i.e., a semiconductor wafer W (hereafterreferred to as a “wafer W”) on which a single-layer film or amulti-layer film is formed.

A power supply device 30 for supplying dual-frequency superposed poweris connected to the lower electrode 20. The power supply device 30includes a first high-frequency power supply 32 for supplying firsthigh-frequency power (plasma generation high-frequency power) with afirst frequency, and a second high-frequency power supply 34 forsupplying second high-frequency power (bias voltage generationhigh-frequency power) with a second frequency that is lower than thefirst frequency. The first high-frequency power supply 32 iselectrically connected via a first matching box 33 to the lowerelectrode 20. The second high-frequency power supply 34 is electricallyconnected via a second matching box 35 to the lower electrode 20.

Each of the first matching box 33 and the second matching box 35 makesthe internal (or output) impedance of the corresponding one of the firsthigh-frequency power supply 32 and the second high-frequency powersupply 34 to match a load impedance. While plasma is being generated inthe chamber 10, each of the first matching box 33 and the secondmatching box 35 makes the internal impedance of the corresponding one ofthe first high-frequency power supply 32 and the second high-frequencypower supply 34 to apparently match the load impedance.

The upper electrode 25 is attached to a ceiling of the chamber 10 via ashield ring 40 covering the periphery of the upper electrode 25. Theupper electrode 25 may be electrically grounded as illustrated inFIG. 1. Alternatively, a variable direct-current power supply (notshown) may be connected to the upper electrode 25 so that adirect-current (DC) voltage is applied to the upper electrode 25.

A gas inlet 45 for introducing a gas from the gas supply 15 is formed inthe upper electrode 25. Also, a diffusion chamber 50 is formed in theupper electrode 25 to diffuse a gas introduced via the gas inlet 45.Further, multiple gas supply holes 55 for supplying a gas from thediffusion chamber 50 into the chamber 10 are formed in the upperelectrode 25. Through the gas supply holes 55, a process gas is suppliedbetween the wafer W placed on the lower electrode 20 and the upperelectrode 25. That is, a process gas from the gas supply 15 is firstsupplied via the gas inlet 45 into the diffusion chamber 50. Then, theprocess gas in the diffusion chamber 50 is distributed to the gas supplyholes 55, and is ejected from the gas supply holes 55 toward the lowerelectrode 20. With the above configuration, the upper electrode 25 alsofunctions as a gas showerhead for supplying a gas.

An evacuation port 60 is formed in the bottom of the chamber 10. Anevacuation device 65 connected to the evacuation port 60 evacuates thechamber 10 and maintains the chamber 10 at a predetermined vacuumpressure.

A gate valve G is provided on a side wall of the chamber 10. The gatevalve G opens and closes a port for carrying the wafer W into and out ofthe chamber 10.

The plasma etching apparatus 1 also includes a controller 100 forcontrolling operations of the entire plasma etching apparatus 1. Thecontroller 100 includes a central processing unit (CPU) 105, and storageareas including a read-only memory (ROM) 110 and a random access memory(RAM) 115.

The CPU 105 performs a plasma etching process according to variousrecipes stored in the storage areas. A recipe includes controlinformation for controlling the plasma etching apparatus 1 to perform aprocess according to process conditions. For example, the controlinformation includes a process time, a pressure (gas discharge),high-frequency power and voltage, flow rates of various process gases,and inner-chamber temperatures (e.g., an upper electrode temperature, achamber side-wall temperature, and an ESC temperature). Recipesindicating programs and process conditions may be stored in a hard diskor a semiconductor memory, or may be stored in a portable,computer-readable storage medium such as a CD-ROM or a DVD that ismounted on a predetermined position of a storage area.

A plasma etching method described later is performed by the exemplaryplasma etching apparatus 1 of the present embodiment described above. Inthis case, the gate valve G is first opened, and the wafer W on which atarget film is formed is carried into the chamber 10 and placed on thelower electrode 20 by, for example, a conveying arm (not shown). Next,the controller 100 controls components of the plasma etching apparatus 1to generate desired plasma. Desired plasma etching is performed by thegenerate plasma according to a plasma etching method described later. Anoverall configuration of the plasma etching apparatus 1 of the presentembodiment is described above.

<Plasma Etching Method>

FIG. 2 is a flowchart illustrating an exemplary plasma etching methodaccording to the present embodiment.

The plasma etching method of the present embodiment performs plasmaetching on an object including an etching-target film and a patternedmask. As illustrated by FIG. 2, the plasma etching method includes afirst step (S1000) of plasma-etching the etching-target film using themask, and a second step (S2000) of depositing a silicon-containing filmusing plasma of a silicon-containing gas on at least a part of a sidewall of the etching-target film etched by the first step.

These steps are described in more detail with reference to FIGS. 3Athrough 3E.

FIGS. 3A through 3E are drawings used to describe an exemplary plasmaetching method of the present embodiment.

In the example of FIGS. 3A through 3E, a plasma etching process isperformed on a semiconductor wafer W including a silicon substrate 150,and an oxide film 155, an ACL film 160, a silicon oxynitride film (SiONfilm) 165, an antireflection film 170 (BARC film 170), and a photoresistfilm 175 that are stacked in this order on a surface of the siliconsubstrate 150. The layer structure of the semiconductor wafer W isbriefly described below.

The silicon substrate 150 is a discoidal thin plate comprised ofsilicon. The oxide film (SiO₂ film) 155 is formed on a surface of thesilicon substrate 150 by, for example, performing a thermal oxidationprocess on the surface. On the oxide film 155, the ACL film 160 isformed. The ACL film 160 is a mask layer and functions as a lower-layerresist film. On the ACL film 160, the SiON film 165 is formed by, forexample, a CVD process or a PVD process. On the SiON film 165, the BARCfilm 170 is formed by, for example, an application process. Further, thephotoresist film 175 is formed on the BARC film 170 by using, forexample, a spin coater. The BARC film 170 includes a polymer resinincluding a pigment that absorbs light with a specific wavelength suchas an ArF excimer laser beam emitted toward the photoresist film 175.The BARC film 170 prevents the ArF excimer laser beam, which passesthrough the photoresist film 175, from being reflected by the SiON film165 or the ACL film 160 and reaching the photoresist film 175 again. Thephotoresist film 175 includes, for example, a positive photosensitiveresin and is altered to have alkali solubility when illuminated by theArF excimer laser beam.

With the semiconductor wafer W configured as described above, thephotoresist film 175 is first patterned as illustrated by FIG. 3A. Thephotoresist film 175 may be patterned using a known photolithographytechnology.

Next, as illustrated by FIG. 3B, the BARC film 170 and the SiON film 165are etched by plasma etching using the patterned photoresist film 175 asa mask.

Any process gas may be used to etch the BARC film 170 and the SiON film165. To etch the BARC film 170 and the SiON film 165 at a high aspectratio and a high etching rate, however, a mixed gas of a fluorocarbon(CF) gas such as carbon tetrafluoride (CF₄) and an oxygen (O₂) gas ispreferably used.

Next, as illustrated by FIG. 3C, the ACL film 160 is etched by plasmaetching using the SiON film 165 as a mask (S1000).

Although any process gas may be used for etching, to prevent bowing andform an opening (hole or trench) with a desired shape, a mixed gas of anoxygen gas (O₂) and a carbonyl sulfide (COS) gas is preferably used.

One problem that may occur in etching the ACL film 160 is “bowing” wherea cross section of an opening of the ACL film 160 in a directionperpendicular to the thickness direction of the ACL film 160 becomeswider than a cross section of an opening of the SiON film 165. Forexample, as illustrated by FIG. 3C, a width H2 of an opening of the ACLfilm 160 (in FIG. 3C, H2 indicates the width of the widest part of theopening) becomes greater than a width H1 of an opening of the SiON film165.

A cause of bowing is briefly described below. In etching, a process gasis converted by high-frequency power into plasma and ions (and radicals)are generated, and the ions bombard an object to be etched. The ions areincident on the object mainly in a vertically downward direction inFIGS. 3A through 3E. However, due to, for example, ion scattering causedby collision of molecules in the plasma, the ions are incident on theobject at an incident angle with respect to the vertically downwarddirection. As a result, the ions bombard a side wall 180 of the ACL film160 and cause bowing. Generally, as illustrated in FIG. 3C, when bowingoccurs, the cross section of a part of the opening of the ACL film 160closer to the SiON film 165 used as a mask becomes larger. In otherwords, the cross section of a top part of the opening of the ACL film160 tends to become larger than the cross section of a bottom part ofthe opening.

To satisfy the recent demand for downsizing semiconductor devices, it ispreferably to prevent the occurrence of even slight bowing. When bowingoccurs, the width of a partition wall between adjacent openings of theACL film 160 becomes insufficient, and a problem such as a mask break,where the ACL film 160 is broken, occurs.

For this reason, in the present embodiment, as illustrated by FIG. 3D, asilicon-containing film 185 is deposited using plasma of asilicon-containing gas on at least a part of the side wall 180 of atleast an etching-target film (the ACL film 160 in the example of FIGS.3A through 3E) at the second step (S2000).

Any silicon-containing gas may be used as long as a silicon-containingfilm can be deposited on at least a part of the side wall 180 of anetching-target film (the ACL film 160 in the example of FIGS. 3A through3E) by plasma CVD (chemical vapor deposition) using thesilicon-containing gas. In the present embodiment, as an example, amixed gas of a silicon-containing gas such as silicon tetrachloride(SiCl₄) or silicon tetrafluoride (SiF₄), a reducing gas such as hydrogen(H₂), nitrogen (N₂), and a diluent gas including an inactive gas such asa noble gas (e.g., helium (He)) is used. With the mixed gas, thesilicon-containing film 185 including silicon, silicon oxide (e.g., SiO,SiO₂), and/or silicon nitride (e.g., Si₃N₄) is deposited on the sidewall 180 of the ACL film 160.

In the second step, a process gas including a silicon-containing gas isconverted by high-frequency power into plasma, and generated ions andradicals are left as a deposit. As described above, due to, for example,ion scattering caused by collision of molecules in plasma, ions areincident on an object at an incident angle with respect to thevertically downward direction in FIG. 3C. For this reason, a largeramount of the silicon-containing film tends to be deposited on a toppart than on a bottom part of the side wall 180 of the ACL film 160.Accordingly, the second step of the present embodiment is an effectiveprocess to correct a “bowing” shape, and makes it possible to form anopening with an excellent vertical shape. Also, the second step canmaintain the critical dimension (CD) of the bottom part. Further,because the amount of the silicon-containing film deposited on thebottom part is smaller than the amount of the silicon-containing filmdeposited on the SiON film 165, it is possible to increase the amount ofremaining mask and to form an opening with a high aspect ratio.

Next, as illustrated by FIG. 3D, the oxide film 155 is etched using afilm structure including the silicon-containing film 185, the SiON film165, and the ACL film 160 on the oxide film 155 as a mask. Asillustrated by FIG. 3E, because an opening with an excellent verticalshape has been formed as a result of the second step, it is alsopossible to reduce bowing and form an opening with an excellent verticalshape by etching the oxide film 155.

In the example of FIG. 3C, the second step is performed after etchingthe ACL film 160 at the first step and thereby exposing the oxide film155 below the ACL film 160. However, the present invention is notlimited to this example. The oxide film 155 may be exposed by graduallyetching the ACL film 160 through the repetition of the first step andthe second step. In more general terms, the second step may be performedwhen bowing occurs during the first step to correct a bowing shape of aside wall, and then the first step (and the subsequent second step) maybe performed again. In this case, the second step may be performed atany appropriate timing before the width of an opening increases due tobowing in the first step and the width of a partition wall betweenadjacent openings becomes insufficient. Also, the first step and thesecond step may be repeated.

Also in the example of FIGS. 3A through 3E, the ACL film 160 is used asan etching-target film, and the second step is performed to correctbowing occurred while etching the ACL film 160. However, the presentinvention is not limited to this example, and a different film may beused as an etching-target film. For example, even when bowing occurswhile etching the oxide film 155 as in FIG. 3E, the second step may beperformed to correct the bowing by depositing a silicon-containing maskon at least a part of a side wall of the oxide film 155.

Next, embodiments performed according to the plasma etching method ofthe present embodiment are described.

First Embodiment

A first embodiment was performed to prove that the plasma etching methodof the present embodiment can correct bowing.

A semiconductor wafer W used in the first embodiment includes thesilicon substrate 150, and the oxide film 155, the ACL film 160, theSiON film 165, the antireflection film 170 (BARC film 170), and thephotoresist film 175 that are stacked beforehand on a surface of thesilicon substrate 150 in this order. Also, before performing the plasmaetching method of the present embodiment, the photoresist film 175 waspatterned to have a predetermined pattern, and the antireflection film170 and the SiON film 165 were etched (or patterned) using thephotoresist film 175 as a mask.

A plasma etching step as the first step and a silicon-containing filmdeposition step as the second step were performed on the semiconductorwafer W prepared as described above.

The first step and the second step were performed under processconditions indicated below.

(Process Conditions of First Step)

-   -   Pressure: 10 mT (1.33 Pa)    -   Power: first high-frequency power/1000 W    -   Potential of upper electrode: 0 V    -   Gas flow rate: O₂ gas/COS gas 200/17 sccm    -   Etching time: 120 sec.        (Process Conditions of Second Step)    -   Pressure: 300 mT (40 Pa)    -   Power: first high-frequency power/250 W, second high-frequency        power/300 W    -   Gas flow rate: SiCl₄ gas/He gas/H₂ gas 50/600/150 sccm    -   Deposition time: 60 sec.

FIGS. 4A and 4B are SEM images used to describe an exemplary effect ofthe plasma etching method of the present embodiment. More specifically,FIG. 4A is a SEM image captured after the first step and before thesecond step, and FIG. 4B is a SEM image captured after the second step.

As is apparent from the comparison of the SEM images of FIGS. 4A and 4B,an opening (hole) with an excellent vertical shape can be obtained byperforming the second step.

Also, for the semiconductor wafer W of each of FIGS. 4A and 4B, a“bowing CD” and a “bottom CD” were obtained. In the present application,the “bowing CD” is defined as the largest width between adjacentpatterns of the ACL film 160, and the “bottom CD” is defined as thewidth of the lower end of an opening.

In FIG. 4A, the “bowing CD” was 130 nm, and the “bottom CD” was 86 nm.In FIG. 4B, the “bowing CD” was 110 nm, and the “bottom CD” was 76 nm.These results indicate that the second step can correct bowing. Theseresults also indicate that a silicon-containing film is more likely tobe deposited on a part having a bowing shape and the bottom CD can bemaintained.

Variation of First Embodiment

As a variation of the first embodiment, the oxide film 155 was alsoetched using the ACL film 160 as a mask.

A semiconductor wafer W used in this variation includes the siliconsubstrate 150, and the oxide film 155, the ACL film 160, the SiON film165, the antireflection film 170 (BARC film 170), and the photoresistfilm 175 that are stacked beforehand on a surface of the siliconsubstrate 150 in this order. Also, before performing the plasma etchingmethod of the present embodiment, the photoresist film 175 was patternedto have a predetermined pattern, and the antireflection film 170 and theSiON film 165 were patterned using the photoresist film 175 as a mask.

A plasma etching step as the first step and a silicon-containing filmdeposition step as the second step were performed on the semiconductorwafer W prepared as described above.

The first step and the second step were performed under processconditions indicated below.

(Process Conditions of First Step)

-   -   Pressure: 10 mT (1.33 Pa)    -   Power: first high-frequency power/1000 W    -   Potential of upper electrode: 0 V    -   Gas flow rate: O₂ gas/COS gas 200/17 sccm    -   Etching time: 2 min.        (Process Conditions of Second Step)    -   Pressure: 300 mT (40 Pa)    -   Power: first high-frequency power/250 W, second high-frequency        power/300 W    -   Gas flow rate: SiCl₄ gas/He gas/H₂ gas 50/600/150 sccm    -   Deposition time: 15 sec.

Plasma etching was performed on the oxide film 155 of the resultingsemiconductor wafer W. The plasma etching was performed ender etchingconditions indicated below.

-   -   Pressure: 40 mT (5.33 Pa)    -   Power: first high-frequency power/1200 W, second    -   high-frequency power/3000 W    -   Potential of upper electrode: 300 V    -   Gas flow rate: C₄F₆ gas/CF₄ gas/Ar gas/O₂ gas 32/24/600/40 sccm    -   Etching time: 150 sec.

FIGS. 5A through 5D are SEM images used to describe another exemplaryeffect of the plasma etching method of the present embodiment. Morespecifically, FIG. 5A is a SEM image captured after the second step, andFIG. 5B is a SEM image captured after the oxide film 155 of thesemiconductor wafer W of FIG. 5A is etched. Also, as comparativeexamples, FIG. 5C illustrates a SEM image captured immediately after thefirst step, and FIG. 5D illustrates a SEM image captured after the oxidefilm 155 is etched without performing the second step.

As is apparent from the comparison of FIGS. 5B and 5D, FIG. 5B of thisvariation, where the second step was performed, indicates that thepresent embodiment makes it possible to correct bowing and necking andform a hole with an excellent vertical shape.

In FIG. 5B, the amount of remaining mask is 506 nm, and an opening width(hereafter referred to as a “top CD”) at the upper end of the oxide film155 is 87 nm. In FIG. 5D, the remaining amount of mask is 446 nm, thetop CD of the oxide film 155 is 100 nm, and the bowing CD of the oxidefilm 155 is 100 nm.

Thus, the results of the first embodiment and the variation of the firstembodiment indicate that the plasma etching method of the presentembodiment makes it possible to reduce necking and bowing, and form asubstantially-vertical, fine hole with a high aspect ratio.

Second Embodiment

In a second embodiment, a relationship between the flow rate of asilicon-containing gas and the amount of a deposited silicon-containingfilm in the second step was confirmed.

A semiconductor wafer W used in the second embodiment includes thesilicon substrate 150, and the oxide film 155, the ACL film 160, theSiON film 165, the antireflection film 170 (BARC film 170), and thephotoresist film 175 that are stacked beforehand on a surface of thesilicon substrate 150 in this order. Also, before performing the plasmaetching method of the present embodiment, the photoresist film 175 waspatterned to have a predetermined pattern, and the antireflection film170 and the SiON film 165 were patterned using the photoresist film 175as a mask.

A plasma etching step as the first step and a silicon-containing filmdeposition step as the second step were performed on the semiconductorwafer W prepared as described above.

The first step and the second step were performed under processconditions indicated below.

(Process Conditions of First Step)

-   -   Pressure: 10 mT (1.33 Pa)    -   Power: first high-frequency power/1000 W    -   Potential of upper electrode: 0 V    -   Gas flow rate: O₂ gas/COS gas 200/17 sccm    -   Etching time: 120 sec.        (Process Conditions of Second Step)    -   Pressure: 300 mT (40 Pa)    -   Power: first high-frequency power/250 W, second high-frequency        power/300 W    -   Gas flow rate: SiCl₄ gas/He gas/H₂ gas variable (10, 30, or 50        sccm)/600/150 sccm    -   Deposition time: 20 sec.

FIGS. 6A through 6D are SEM images used to describe another exemplaryeffect of the plasma etching method of the present embodiment. Morespecifically, FIG. 6A is a SEM image of the present embodiment obtainedby setting the flow rate of the SiCl₄ gas at 10 sccm in the second step,FIG. 6B is a SEM image of the present embodiment obtained by setting theflow rate of the SiCl₄ gas at 30 sccm, and FIG. 6C is a SEM image of thepresent embodiment obtained by setting the flow rate of the SiCl₄ gas at50 sccm. Also, FIG. 6D is a SEM image of a comparative example where thesecond step is not performed.

In FIGS. 6A through 6D, the “bowing CD” is 120 nm, 117 nm, 117 nm, and124 nm, respectively. Also in FIGS. 6A through 6D, the “bottom CD” is 80nm, 76 nm, 76 nm, and 84 nm, respectively. These results indicate thatthe deposition rate of the silicon-containing film 185 increases as theflow rate of the silicon-containing gas increases. However, as indicatedby FIG. 6C, this also causes the opening to be closed by thesilicon-containing film 185 and reduces the deposition rate in the hole.

Thus, the results of the second embodiment indicate that the depositionrate of a silicon-containing film is increased by increasing the flowrate of a silicon-containing gas in the second step of the plasmaetching method of the present embodiment.

Third Embodiment

In a third embodiment, the oxide film 155 is selected as an etchingtarget film.

A semiconductor wafer W used in the third embodiment includes thesilicon substrate 150, and the oxide film 155, the ACL film 160, theSiON film 165, the antireflection film 170 (BARC film 170), and thephotoresist film 175 that are stacked beforehand on a surface of thesilicon substrate 150 in this order. Also, before performing the plasmaetching method of the present embodiment, the photoresist film 175 waspatterned to have a predetermined pattern, and the antireflection film170 and the SiON film 165 were patterned using the photoresist film 175as a mask.

Using the semiconductor wafer W prepared as described above, a plasmaetching step on the ACL film 160 was performed as the first step and asilicon-containing film deposition step on a side wall of the ACL film160 was performed as the second step. Further, a plasma etching step onthe oxide film 155 was performed as a first′ step, and asilicon-containing film deposition step on side walls of the ACL film160 and the oxide film 155 was performed as a second′ step.

The respective steps were performed under process conditions indicatedbelow.

(Process Conditions of First Step)

-   -   Pressure: 10 mT (1.33 Pa)    -   Power: first high-frequency power/1000 W    -   Potential of upper electrode: 0 V    -   Gas flow rate: O₂ gas/COS gas 200/17 sccm    -   Etching time: 120 sec.        (Process Conditions of Second Step)    -   Pressure: 300 mT (40 Pa)    -   Power: first high-frequency power/250 W, second high-frequency        power/300 W    -   Gas flow rate: SiCl₄ gas/He gas/H₂ gas 50/600/150 sccm    -   Deposition time: 15 sec.        (Process Conditions of First′ Step)    -   Pressure: 40 mT (5.33 Pa)    -   Power: first high-frequency power/1200 W, second high-frequency        power/3000 W    -   Potential of upper electrode: 300 V    -   Gas flow rate: C₄F₆ gas/CF₄ gas/Ar gas/O₂ gas 32/24/600/40 sccm    -   Etching time: 160 sec.        (Process Conditions of Second′ Step)    -   Pressure: 300 mT (40 Pa)    -   Power: first high-frequency power/250 W, second high-frequency        power/300 W    -   Gas flow rate: SiCl₄ gas/He gas/H₂ gas 50/600/150 sccm    -   Deposition time: 20 sec.

Plasma etching was performed on the oxide film 155 of the resultingsemiconductor wafer W. The plasma etching was performed under etchingconditions indicated below.

-   -   Pressure: 40 mT (5.33 Pa)    -   Power: first high-frequency power/1200 W, second high-frequency        power/3000 W    -   Potential of upper electrode: 300 V    -   Gas flow rate: C₄F₆ gas/CF₄ gas/Ar gas/O₂ gas 32/24/600/40 sccm    -   Etching time: 50 sec.

FIGS. 7A and 7B are SEM images used to describe another exemplary effectof the plasma etching method of the present embodiment. Morespecifically, FIG. 7A is a SEM image captured after performing theplasma etching on the oxide film 155 after the second′ step, and FIG. 7Bis a SEM image of a comparative example where the second′ step was notperformed.

In FIG. 7A, the largest width between adjacent patterns is 97 nm, andthe amount of remaining mask is 414 nm. In FIG. 7B, the largest widthbetween adjacent patterns is 107 nm, and the amount of remaining mask is410 nm.

Thus, the results of the third embodiment indicate that even when a filmother than the ACL film is etched as an etching target film, a bowingshape can be corrected by depositing a silicon-containing film on a sidewall of an opening by the second step.

Fourth Embodiment

In a fourth embodiment, the first step and the second step wereperformed multiple times on one etching target film.

Using the semiconductor wafer W obtained in the third embodiment, aplasma etching step on the oxide film 155 was performed as a first″ step(which corresponds to a third step in the claims), and asilicon-containing film deposition step on side walls of the ACL film160 and the oxide film 155 was performed as a second″ step (whichcorresponds to a fourth step in the claims).

The respective steps were performed under process conditions indicatedbelow.

(Process Conditions of First″ Step)

Plasma etching was performed on the oxide film 155 of the resultingsemiconductor wafer W under the following etching conditions.

-   -   Pressure: 40 mT (5.33 Pa)    -   Power: first high-frequency power/1200 W, second high-frequency        power/3000 W    -   Potential of upper electrode: 300 V    -   Gas flow rate: C₄F₆ gas/CF₄ gas/Ar gas/O₂ gas 32/24/600/40 sccm    -   Etching time: 50 sec.        (Process Conditions of Second″ Step)    -   Pressure: 300 mT (40 Pa)    -   Power: first high-frequency power/250 W, second high-frequency        power/300 W    -   Gas flow rate: SiCl₄ gas/He gas/H₂ gas variable (10, 30, or 50        sccm)/600/150 sccm    -   Deposition time: 20 sec.

Also, plasma etching was performed on the oxide film 155 of thesemiconductor wafer W after the second″ step. The plasma etching wasperformed under etching conditions indicated below.

-   -   Pressure: 40 mT (5.33 Pa)    -   Power: first high-frequency power/1200 W, second high-frequency        power/3000 W    -   Potential of upper electrode: 300 V    -   Gas flow rate: C₄F₆ gas/CF₄ gas/Ar gas/O₂ gas 32/24/600/40 sccm    -   Etching time: 50 sec.

FIGS. 8A and 8B are SEM images used to describe another exemplary effectof the plasma etching method of the present embodiment. Morespecifically, FIG. 8A is a SEM image captured after performing theplasma etching on the oxide film 155 after the second″ step, and FIG. 7Bis a SEM image of a comparative example where the second″ step was notperformed.

In FIG. 8A, the largest width between adjacent patterns is 103 nm. InFIG. 8B, the largest width between adjacent patterns is 117 nm.

Thus, the results of the fourth embodiment indicate that plasma etchingcan be gradually performed while correcting a bowing shape, by repeatingthe first step and the second step.

The present invention is not limited to the embodiments described above,and variations and modifications may be made depending on applicationswithout departing from the scope of the present invention.

The present application claims priority from Japanese Patent ApplicationNo. 2013-102969 filed on May 15, 2013, the entire contents of which arehereby incorporated herein by reference.

EXPLANATION OF REFERENCE NUMERALS

-   -   1 Plasma etching apparatus    -   10 Chamber    -   15 Gas supply    -   20 Lower electrode    -   25 Upper electrode    -   30 Power supply device    -   32 First high-frequency power supply    -   33 First matching box    -   34 Second high-frequency power supply    -   35 Second matching box    -   40 Shield ring    -   45 Gas inlet    -   50 Diffusion chamber 50    -   55 Gas supply hole    -   60 Evacuation port    -   65 Evacuation device    -   100 Controller    -   105 CPU    -   110 RAM    -   150 Silicon substrate    -   155 Oxide film    -   160 ACL film    -   165 SiON film    -   170 Antireflection film    -   175 Photoresist film    -   180 Side wall    -   185 Silicon-containing film    -   G Gate valve    -   W Wafer

The invention claimed is:
 1. A plasma etching method for plasma-etchingan object including an oxide film, an amorphous carbon layer film formedon the oxide film, an inorganic film formed on the amorphous carbonlayer film, and a patterned first mask, the method comprising: a firststep of plasma-etching the inorganic film using the first mask; a secondstep of etching the amorphous carbon layer film using the etchedinorganic film as a second mask and thereby exposing the oxide film; anda third step of, after exposing the oxide film by the second step,depositing a silicon-containing film using plasma of asilicon-containing gas on an upper surface of the second mask and atleast a part of a side wall of the etched amorphous carbon layer film,wherein as a result of the second step, a thickness of a top part of theside wall of the etched amorphous carbon layer film that is closer tothe second mask becomes less than a thickness of a bottom part of theside wall of the etched amorphous carbon layer film that is closer tothe oxide film; and the third step is performed such that a thickness ofthe silicon-containing film deposited on the top part of the side wallof the etched amorphous carbon layer film becomes greater than athickness of the silicon-containing film deposited on the bottom part ofthe side wall of the etched amorphous carbon layer film.
 2. The plasmaetching method as claimed in claim 1, wherein the silicon-containing gasincludes one of silicon tetrachloride and silicon tetrafluoride, and areducing gas.
 3. The plasma etching method as claimed in claim 1,wherein in the second step, the amorphous carbon layer film is etchedwith plasma of a process gas including an oxygen gas and a carbonylsulfide gas by using the etched inorganic film as the second mask. 4.The plasma etching method as claimed in claim 1, further comprising: afourth step of plasma-etching the oxide film using a third maskincluding the amorphous carbon layer film; and a fifth step ofdepositing a silicon-containing film using plasma of asilicon-containing gas on at least a part of a side wall of the oxidefilm etched by the fourth step.
 5. The plasma etching method as claimedin claim 4, wherein in the fourth step, the oxide film is plasma-etchedusing plasma of a process gas including a fluorocarbon gas.
 6. Theplasma etching method as claimed in claim 4, wherein the fourth step andthe fifth step are repeated.
 7. The plasma etching method as claimed inclaim 1, wherein the object further includes an antireflection filmformed on an upper side of the inorganic film, and the first mask is apatterned resist film formed on the antireflection film; and wherein inthe first step, the antireflection film and the inorganic film areetched with plasma of a process gas including a fluorocarbon gas byusing the resist film as the first mask.
 8. The plasma etching method asclaimed in claim 1, wherein in the third step, a process gas includingthe silicon-containing gas is converted by high-frequency power into theplasma including ions and radicals so that, due to ion scattering causedby collision with molecules in the plasma, the ions and the radicals areincident on the side wall of the etched amorphous carbon layer film atan incident angle with respect to a vertically-downward direction and alarger amount of the silicon-containing film is deposited on the toppart of the side wall than on the bottom part of the side wall.